Desmodinosides A-E: New Flavonoid C-glycosides from Desmodium heterocarpon var. stigosum with hepatoprotective and antifungal activity

Five new flavonoid C-glycosides named desmodinosides A-E (1-5) and one known compound, apigenin 6-C-β-d-xylopyranosyl-2''-O-β-D-glucopyranoside (6) have been isolated from the methanol extract of the aerial parts of Desmodium heterocarpon var. stigosum. These compounds were determined by 1D and 2D-NMR and HR-MS spectroscopies. The methanol extract of this plant, in particular, demonstrated hepatoprotection and antifungal inhibition. This extract has a remarkable hepatoprotection and activity-dose response with an EC50 of 43.07 μg/mL. The hepatoprotective effect on human liver hepatoma cells (HepG2) of the isolated flavonoid C-glycosides 1-6 was observed. Desmodinosides A-C (1-3) were found to exhibit moderate hepatoprotective activity on HepG2 cells. Of these, compound 2 showed the best hepatoprotective activity with an EC50 value of 74.12 μg/mL. While compounds 1 and 3 displayed EC50 values of 271.21 and 211.99 μg/mL, respectively. Quercetin, a positive control, also caused an EC50 value of 36.42 μg/mL. In addition to having hepatoprotective effect, the methanol extract had an inhibitory effect on the growth of oomycete; it inhibited Phytophthora infestans with IC50 of 13.3 μg/mL and IC90 of 78.7 μg/mL. The oomycete inhibition was directly attributed to compounds 5 and 6, which significantly inhibited P. infestans with IC50 values of 27.4 and 24.7 μg/mL, respectively. Both 5 and 6 and methanol extract were active against P. infestanse in a dose-dependent manner. Our study demonstrated for the first time the new flavonoid C-glycosides from D. heterocarpon var. stigosum and their novel pharmacological properties. The study findings also suggest the plant extract and its metabolites could be used as a new botanical source of bioactive compounds.

Chemical constituents of Antidesma bunius aerial parts and the anti-AGEs activity of selected compounds

Thirty-three natural products were isolated from the aerial parts of Antidesma bunius, Euphorbiaceae, a plant used in Vietnamese traditional medicine against rheumatoid arthritis. All compounds were reported the first time for this species, and nine constituents resembled undescribed natural products, noticeably three coumarinolignans with 2,2-dimethyl-1,3-dioxolane moiety, two cyclopeptides, and two furofuran-type lignans connected with a phenylpropanoid moiety. The individual structures were elucidated by combining NMR and MS data, and their configuration was established by NOESY and ECD experiments and NMR calculations. Compounds with sufficient amount were analyzed for their inhibition of advanced glycation endproducts (AGEs) formation, metabolites involved in many diseases like Alzheimer, joint diseases or diabetes. With IC₅₀ values below 0.2 mM rutin and p-hydroxyphenethyl trans-ferulate showed to be moderately active, both still being 10-times more active than the positive control aminoguanidine.

Chemical constituents of Desmodium triflorum and their antifungal activity against various phytopathogenic fungi

In the course of finding new antifungal natural compounds against plant pathogens, the methanol extract of Desmodium triflorum was investigated phytochemically. From n-butanol-soluble fraction, seven compounds (1-7) were isolated and structurally elucidated. Of which, six compounds belong to flavone 6- or 8-C-glycoside class (1-6). Three major compounds (1-3) exhibited moderate in vitro antifungal activity against Sclerotium rolfsii, Fusarium oxysporum f. sp. cubense, and Phytophthora palmivora. Compound 1 (IC₅₀ = 162.1 μg/mL) was most active against S. rolfsii in a dose-dependent manner. At 300 μg/mL, compounds 1 and 2 significantly inhibited P. palmivora, whereas compound 3 lacked effectiveness. In addition, the nanoemulsion of the methanol extract with a droplet size of 12.2 nm displayed an excellent inhibition against S. rolfsii and P. palmivora compared with the normal extract. The presence of 1 (0.846%) and 2 (0.759%) in the methanol extract may attribute to the antifungal activity of D. triflorum. These results proved the potential of D. triflorum and its C-glycoside flavonoids against phytopathogenic fungi for the first time. Besides, an enhancement in the effectiveness of nanoemulsion containing D. triflorum extract against the fungi was confirmed. The structural characteristics of 1 and 2 could be considered to develop new fungicidal substances in the future.

Terpenoids from the Stems of Fissistigma polyanthoides and Their Anti-Inflammatory Activity

Twelve new terpenoids (1-12) were isolated from the stems of Fissistigma polyanthoides, an anti-inflammatory medicinal plant traditionally used in Vietnam. Most of them (1-9) possess a sesquiterpenoid backbone (e.g., guaiane, germacrane, and cadinane) connected to a 2'-O-trans-cinnamoyl)-β-d-glucopyranose moiety, which is rare in Nature. Among them, compounds 4 (5/8-fused ring) and 6 (spiran [4,5] ring) represent uncommonly rearranged sesquiterpenoids. Compounds 10-12 are a novel monoterpene and two megastigmane derivatives, respectively. The individual structures were elucidated by combining NMR and MS data, and their configuration was established in NOESY and ECD experiments. Compounds 1-9 were also examined for their potential to interact with nuclear factor-kappa B activator protein 1 (NF-κB/AP-1) signaling by using the myelomonocytic reporter cell line THP-1Blue-CD14. Compounds 1-5 showed dose-dependent inhibitory effects [IC₅₀ 13.7 μM (1) to 49.0 μM (5)] on lipopolysaccharide-stimulated cells. However, compounds 1 to 4 also negatively affected cell viability in the same concentration range, while compound 5 was less potently cytotoxic.

Phenolic compounds from the stems of Fissistigma polyanthoides and their anti-oxidant activities

The stems of Fissistigma polyanthoides (A.DC.) Merr. are traditionally used for the treatment of rheumatism and for recuperating women after childbirth. In our continuous phytochemical investigation of this plant, four new (1, 2, 5, and 19) and fifteen known (3, 4, and 6-18) phenolic compounds were isolated. The structures of all compounds were elucidated based on extensive spectroscopic analyses (1D-, 2D-NMR, and MS), and in comparison with reported literature data. The new natural products showed to be two poly-methoxylated chalcones (1 and 2) and two flavonoid glycosides, with 19 containing an uncommon sugar moiety (quinovose). Compounds with sufficient amount were tested for their anti-oxidant activity in a cell-based assay using the human bronchial epithelial cell line BEAS-2B. The compounds' capacity to inhibit the peroxyl radical triggered formation of dichlorofluorescein (DCF) was investigated in a dose-dependent manner. Both, anti-oxidant (3, 4, 6, 8-12, and 14) and pro-oxidative (5 and 16) properties were found for the investigated substances. The half maximal concentrations (IC₅₀) for the inhibition of ROS formation ranged between 18.8 μM and 63.5 μM. Compounds, which acted protectively in the cellular antioxidant activity (CAA) assay and did not negatively affect cell viability, could be interesting targets for further investigations.

Phytochemical and analytical characterization of constituents in Urceola rosea (Hook. & Arn.) D.J. Middleton leaves

In Vietnam and China the leaves of Urceola rosea are widely used as herbal remedy and food. However, in contrast to the plants stem, little information was available on major constituents. In this study, the first in-depth phytochemical investigation of U. rosea leaves is described, which resulted in the isolation of thirteen compounds, mainly flavonoids (kaempferol and quercetin derivatives) and triterpenes. Furthermore, an analytical procedure for the quantification of five major compounds was developed. The HPLC separation was performed on a Synergi MAX-RP column using acetonitrile and 0.1% formic acid as mobile phase. Method validation confirmed that the assay shows good linearity (R²≥0.9997), precision (intra-day R.S.D≤4.31%, inter-day R.S.D≤3.52%) and accuracy (recovery rates ranged from 96.8 to 102.6%). Detection limits were always lower than 0.07μg/mL. The analysis of several plant samples revealed distinct differences, as for example the content of total phenolics varied from 0.44 to 1.73%.

In Vitro Anti-Leishmanial Activity of Essential Oils Extracted from Vietnamese Plants

Leishmania mexicana is one of the pathogens causing cutaneous leishmaniasis which is associated with patient morbidity. In our researches for new safe and effective treatments, thirty-seven essential oils (EOs) extracted from Vietnamese plants were screened in vitro for the first time on Leishmania mexicana mexicana (Lmm) promastigotes at the maximum concentration of 50 nL/mL. Active EOs were also analyzed for cytotoxicity on mammalian cell lines (WI38, J774) and their selectivity indices (SI) were calculated. Their composition was determined by GC-MS and GC-FID. Our results indicated that EOs extracted from Cinnamomum cassia, Zingiber zerumbet, Elsholtzia ciliata and Amomum aromaticum, possessed a moderate anti-leishmanial activity, with IC₅₀ values of 2.92 ± 0.08, 3.34 ± 0.34, 8.49 ± 0.32 and 9.25 ± 0.64 nL/mL respectively. However, they also showed cytotoxicity with SI < 10. The most promising EO was extracted from Ocimum gratissimum, displaying an IC₅₀ of 4.85 ± 1.65 nL/mL and SI > 10. It contained 86.5% eugenol, which was demonstrated to be effective on Lmm with IC₅₀ of 2.57 ± 0.57 nL/mL and not toxic on mammalian cells, explaining the observed activity.